Zone Alpha - Green Globe
Alright... now that you've started the game, the very first thing you'll want to do is capture the first enemy that comes up, officially known as "Rei NESIUM". This will split into two which provide some small firepower in the same direction as the Silver Hawk's own fire.
The very first formations will give you one of every powerup, equipping you with the bare minimum essentials you need to get going. If you missed any of them, that is a clear cut indicator that you messed up and need to reset. Missing any powerups can be detrimental to your run, really.
To get double score with Rei NESIUM, taking out most of the smaller enemies is trivial since they're one-hit wonders, but larger ones like the so-called "Rei SOID" take more hits, which the capture's bullets can't land on time. In the best case scenario, you'd use your main firepower to quickly weaken the enemy, then destroy it with the capture's bullets.
Pretty soon, you'll come across a divergence. The Darius series has been well noted for its branched zone structure, but G-Darius takes this a step further as it splits zones into different areas at the midpoint. To select an area, you move the Silver Hawk into one half of the screen and hold that position until the timer expires; the on-screen indicators make that self-explanatory.
There's also the first occurrence of an enemy barricaded by those gold pieces I was talking about earlier. As I said, you need to use your normal firepower to destroy them. This may look like the miniboss, but it's not.
Deciding which area to stick to doesn't simply add visual variety; it also affects which kinds of enemies you'll be up against, the terrain you may have to traverse, what powerups will be available, and what attacks the zone's boss will have. If you were to select Area B, you'd dive through an underwater cavern, acquire twin bombs, and get an extra unit for your arm barrier. However, this area has no captain and it doesn't have as many red powerups.
In general, I'd favor going to Area A, which is what this route will be using. From here, it'll seem like there's so many things flying at you all at once, but it's really not so bad. Enemies often fire in the direction which you're standing at, so a common STG technique known as tap-dodging, where you just move in a direction a little bit at a time, comes into play. Say you have space to move up to the top of the screen; if you were to scurry there right away, you might get cornered. But, if you quickly tap upwards for a split second, wait, and then tap up again, it should give you more room to evade the overall wave of attacks headed towards you.
But what's more important than that is memorizing where all the enemy formations will appear from. This may be difficult to do when you're first encountering them, so it helps a lot to record your gameplay. G-Darius HD has a built-in replay system, so if you don't have powerful enough recording equipment, you can use that function.
Assuming you haven't somehow wasted your initial capture already, here is a good place to charge your alpha beam: right after clearing the one formation coming from the top right and downward as you're about to rise above the arch. As you move up to the top left of the screen, hold down the regular shot button until you see a blue flash coming from the front of the Silver Hawk, then immedediately release and rapid fire to ensure your beam lasts long enough to clear out the following formations.
The end of this beam should line up perfectly with the entry of the first captain. When you move to the center, it will try to dodge you either up or down depending on where you're positioned. You can simply point blank its helmet until it breaks, and then capture it, as the homing missiles it fires can be destroyed by your normal fire.
Normally, this captain will shoot out homing missiles towards your enemies, but by performing a quick movement (down, down+right, right) followed by pressing the shot button, it will lock in place and fire a powerful wave laser. Basically, you'd have to make a quick, quarter-circular, counter-clockwise motion with some directional controls; an arcade stick is definitely the easiest to work with as the game was initially designed around that. Also be mindful to not let the captain get hit too much here.
Huge Battleship: Eclipse Eye
This thing is easy. You could get away with just rapid firing at it or immediately beaming your captain for a quick kill, but it's not as rewarding. Remember, we love to do things the hard way.
Don't hold rapid fire here. Start off by slowly tapping the normal shot button just to destroy the little rockets that spew out of Eclipse Eye's jaws. You'll notice that one press of the shot button fires several bullets.
Once that pattern's finished, don't shoot. The boss will fire six times in three directions, aiming at where you were last standing. Move out of the way up or down a bit and stand there. Eclipse Eye will do this again two more times, adjusting its aim to your new location; again, dodge. It's good to try to help your captain avoid these shots as well, but it should be okay if it takes some hits from this as well. If, however, your captain is destroyed by this pattern, you may have caused it to ram into too many enemies earlier, or the other way around.
This next pattern is also straightforward. These wide, spinning projectiles can be destroyed by your shots, so slowly tap the shot button some more.
If you're really crafty, you can try to break off one of the eyes here as Eclipse Eye is about to turn around, either by tapping the shot button faster or using the First Captain's wave laser. It's not required, but it does give you some extra points.
This next pattern can be really dangerous for your captain, as these larger missiles will rapidly drain its energy if it is in contact with them. For this reason, I just try to create a few homing missiles, and right before the enemy's missiles enter the same layer as the Silver Hawk, I charge the alpha beam and keep it held down. From there, it's just a matter of evading the other missiles. They'll slowly move around trying to get into position, then rapidly charge at you in a fixed direction.
Do you see those red light rays closing in on Eclipse Eye? That means it's getting ready to fire a beta beam. You'll hear a distinct noise indicating this as well. It may take some time to get used to the timing, and you don't have to time your beam exactly with the start of its own, but when it fires, you'll want to release your beam, hold rapid fire, and get into the position of its beam. There, you've got yourself a double counter and secured victory!
From here, you can select the next zone. I've seen many players suggest the Lambda route (all top zones), but here I'll go on the Nu route, taking inspiration from Smraedis. Besides, Tripod Sardine is a very nice guy, and we wouldn't want his head to be blown off, would we???